We seek to isolate and characterize anti-ricketic sterol-binding proteins in blood and tissue, and explore their role in the transport and action of these sterols. Employing binding progeins, or antisera, we shall develop practical methods for the quantitation of anti-ricketic sterols in serum. BIBLIOGRAPHIC REFERENCES: Rohanasathit, S., and Haddad, J.G. Hepatic Accumulation of vitamin D and 25-hydroxyvitamin D3, Biochim. et Biophys. Acta 421:12, 1976. Hillman, L., and Haddad, J.G. Perinatal vitamin D metabolism III. Factors influencing late gestational human serum 25-hydroxyvitamin D., Am. J. Ob. & Gyn 125:196, 1976.